A conventional wavelength division multiplexed network can use specific software to determine key performance parameters of an optical network. These key performance parameters can comprise a maximum transmission capacity achievable between different locations, i.e. nodes of the optical network, or the available operating margin corresponding to a given capacity on a given optical link of the optical network. The maximum transmission capacity achievable between different locations of the network can, for instance, be represented by the sum of data rates carried by individual wavelengths each comprising a specific modulation format, a symbol rate as well as overhead for forward error correction FEC. The available operating margin on any given wavelength can be expressed as a difference between the required and available optical signal to noise ratio (OSNR), a signal to noise ratio (SNR), a Q factor or any other performance metric serving to define a margin of safety for the network operator to account for unforeseen degradations that can occur in the optical network during its operation, or to allocate a margin for future extensions of the optical network. Since different wavelengths transmitted through the optical network between the same two end-points can have a different performance, there are usually different margins for different wavelengths.
Relevant parameters for designing the optical network are the characteristics of the optical fibers along each transmission route such as fiber loss between adjacent network nodes, fiber chromatic dispersion, effective area, and connector loss. Accurate knowledge of these parameters requires complex equipment and measurement methods and characterization efforts which are quite costly and time-consuming for WDM optical networks. Therefore, approximations can be used in the network planning phase and the resulting network capacity has a degree of uncertainty which can be high enough to generate one of two equally undesirable scenarios. The first scenario is that the estimated network capacity cannot be achieved due to worse fiber link parameters than assumed. The other undesirable scenario is that a higher capacity is achievable than in the planned design of the network. In this case, the network operator cannot maximize the use of the available resources. Network designers tend to use a conservative approach in the planning process to avoid the first undesirable scenario which leads to a higher likelihood of an optical network using less capacity than could be achieved. Another consequence is that the available margin in the optical network is unknown at the time of deployment of the optical network. Therefore, commercial optical networks may be either under-utilized, or may not support the eventual maximum transmission capacity assumed in the planning phase.
The uncertainty about the potential transmission capacity and available margin can be resolved at the time of deployment of the network if the available optical spectrum is filled with signals originating and terminating at flexible data rate transponders. As a basic unit of the DWDM system, a transponder has a client side and a network side, whereby one or several client signals received from a router or switch are multiplexed to higher data rates and converted to a WDM signal on the network side, capable of longer distance transmission than the client optics. Conversely, the line side received signal is demultiplexed and converted to a shorter-reach client signal facing the router or switch. The flexible data rate transponders can be set to various modulation formats, symbol rates, channel spacing and can measure a link performance, e.g. as a bit error ratio BER, or as signal to noise ratio, SNR. In this case, the major impairments incurred across the optical transmission link, particularly amplified spontaneous emission, ASE, noise and nonlinear noise are all present from the initial turn-up of the optical system and the approximate estimation of the maximum capacity derived from simulations or calculations can be replaced by actual measurements. The data rate can be adjusted independently on every wavelength. A channel spacing can be adjusted accordingly and a maximum capacity can be determined empirically. Similarly, an operating margin for a given data rate on a given wavelength can be determined using performance metrics.
However, in most applications, the network operator of the optical network does not need the complete transmission capacity at the time of initial deployment and may not provide real data rate transponders for the sole purpose of establishing a maximum attainable transmission capacity. This leaves the network operator of the optical network with an uncertainty with regard to the available capacity and available margin.
Accordingly, there is a need to provide a method and apparatus for determining a maximum transmission capacity within an optical network efficiently and with a minimum number of transponders.